The Ada Information Clearinghouse website http://www.adaic.org/learn/materials/, maintained by the Ada Resource Association, contains links to a variety of training materials (books, articles, etc.) that can help in learning Ada. The Development Center page http://www.adacore.com/knowledge on AdaCore's website also contains links to useful information including vides and tutorials on Ada.

The most comprehensive textbook is John Barnes' Programming in Ada 2012, which is oriented towards professional software developers.